The present invention relates to a device for radiating an ultrasound into a material by means of using an assembly composed of a piezoelectric substrate, input- and output interdigital transducers for delay-line oscillation, and another at least one interdigital transducer for ultrasound radiation into a material.
Popularly, a thickness mode piezoelectric transducer, of which operation frequency is dependent on the thickness of a piezoelectric substrate, is used for emitting an acoustic wave. However, such a conventional type of transducer has a difficulty in oblique incidence of the ultrasound into a liquid.
When the piezoelectric substrate is in contact with a liquid, an interdigital transducer (IDT) on the piezoelectric substrate is useful. By use of the IDT on the piezoelectric substrate, sufficiently thicker compared with the wavelength of a surface acoustic wave (SAW) thereon, the SAW propagates in the form of a leaky wave that is mode-converted to a longitudinal wave into the liquid. In this way, the IDT operates at a liquid-solid boundary as a leaky-wave transducer for bulk wave radiation into the liquid. However, the leaky SAW traveling on a sufficiently thick substrate compared with the wavelength has only one mode without velocity dispersion. Thus, a conventional transducer such as the IDT for the leaky SAW has a problem of a limited ultrasound-radiation angle.
An ultrasound-signal radiating device (U.S. Pat. No. 6,317,389) and a device for ultrasound radiation into a material (U.S. Pat. No. 6,360,611) were provided in order to enable a multi-modes operation at a high frequency. These conventional devices, suitable for radiating an ultrasound into a material, for example, a cellular tissue, are excellent in adjusting of radiation angle and sweeping of ultrasound beam. However, these conventional devices have a difficulty in radiation of ultrasound beam reaching the bottom of a material with a high efficiency. In addition, these conventional devices have a difficulty in continuous driving at a suitable frequency while moving itself on a surface of a material, of which the depth changes.